Cardiovascular hypertension has been induced in rats by administration of the oral contraceptive, Enovid. The projects described here are designed: (a) to develop an experimental model for production of hypertension using oral contraceptives and their constituents, particularly mestranol and norethynodrel; (b) to establish a dose-response relationship between dose of oral contraceptive administered and elevation of blood pressure; (c) to study the reversibility of hypertension induced by oral contraceptives when the drug is withdrawn; (d) to study the effect of oral contraceptives and their constituents on the rate of development of hypertension induced in rats genetically or by renal manipulation; (e) to study the effect of oral contraceptives and their consitutents on serum electrolyte concentrations, food and fluid intakes, growth rate, thyroid function and organ morphology and histology; (f) to explore some possible mechanisms by which oral contraceptives may induce hypertension including: effects on spontaneous intake and taste threshold for NaCl solution, urinary excretion of sodium and potassium during acute diuretic studies, sodium and potassium exchanges during chronic drug treatment, peripheral vascular response to acute administration of catecholamines and angiotensin II, renal content of renin, plasma concentrations of renin and renin substrate, and adrenal secretion of aldosterone.